Pseudomonas putida catalyzes the incorporation of one molecule of oxygen into toluene to form cis-1(S), 2(R)-dihydroxy-1,2-dihydrotoluene. The enzyme system catalyzing this reaction has been resolved into three protein components each of which has been purified and characterized. The three components are: Ferredoxin TQL reductase, a flavoprotein that transfers electrons from NADH to the second component, ferredoxin TOL. Ferredoxin TOL is a (2Fe-2S*) iron sulfur protein that transfers electrons to the terminal oxygenase component, ISPTOL. Current studies are directed toward understanding the details of electron transport in this multienzyme system and the mechanism of enzymatic oxygen fixation into the benzenoid nucleus. Pseudomonas putida, NCIB 9816 oxidizes naphthalene to cis-1(R), 2(S)-dihydroxy-1,2-dihydronaphthalene. This reaction is also catalyzed by a dioxygenase that is also a multienzyme system. Experiments in progress are directed towards the purification and characterization of the individual protein components.